U-RHYTHM, www.u-rhythm.co.uk, is a groundbreaking wearable diagnostic clinical research device at the Bristol Medical School that uses micro-dialysis to sample hormones directly from human interstitial fluid at closely-space intervals throughout the day and night, monitoring the dynamics of hundreds of metabolites and advancing the field of endocrinology[1]. However, ultra-hydrophobic sex hormones cannot be currently detected due to a combination of their low concentrations and their adsorption to the device tubing. Here, we propose a first comprehensive XRR study at the air-water interface to evaluate the F127 Langmuir monolayer structure due to molecular interactions between F127 monolayers and sex hormones with various molecular architectures (Fig. 1), at different surface pressures, temperatures and concentrations. Such fundamental insights from the model system will provide critical nanostructural evidence for the proposed mechanism for enabling enhanced capacity of the U-RHYTHM t